Conventionally, a system has been known that irradiates the light on an object such as, for example, a product so as to create a preferable lighting environment and then takes an image of the object by the use of an image-taking device such as a CCD camera so that appearance check or mark reading can be conducted automatically.
In accordance with this system, in case that the light has to be irradiated also from a direction coaxial with an observation axis of the image-taking device, conventionally a half mirror is arranged at an angle of 45 degree on the observation axis and the light is irradiated on the half mirror from a direction orthogonal to the observation axis. With this arrangement, while the light emitted from a light source is reflected on the half mirror and travels toward a direction coaxial with the observation axis and then is irradiated on the object, the light from the object reaches the image-taking device by passing the half mirror, which makes it possible to take an image of the object. However, with this arrangement, since the half mirror has to be arranged at the angle of 45 degree, a size of the system as a whole becomes bulky especially in a direction of the observation axis and it is difficult to approach the image-taking device to the object because the half mirror intervenes between the image-taking device and the object.
Then, as shown in patent document 1, the present claimed inventor has developed an innovative thin plate-shaped light irradiation device that can be inserted in a direction orthogonal to the observation axis, which makes it possible to downsize the system drastically and to take an image of the object in a closeup mode for the first time.
More concretely, the light irradiation device is so arranged that multiple microscopic reflecting members are arranged on an opposite object facing surface of a transparent plate so as to form a space between each of the reflecting members and the LED light is introduced into the transparent plate through a side surrounding end surface of the transparent plate. The light travels inside the transparent plate while being total-reflected, a part of which is reflected on the reflecting members and irradiated toward the object from the transparent plate. An image-taking device can take an image of the object without almost any influence from the reflecting members, since the reflecting members will not fundamentally be an obstacle to taking an image like we can see a bright room through a screen.
Patent document 1: Japan patent laid open number 2003-98093